By studying DNA fine structure and physical properties at dinucleotide step level, we have proposed and published that, besides W-C pairing Hydrogen bonds, DNA duplex should contain regular Inter-Base-Pair hydrogen bonds (IBP H-Bonds), which result from the recent studying about non-planarity of amino groups in DNA duplex.By analyzing the IBP H-Bonds containing DAN helical fragments of defined-sequence oligonucleotides, we found that there are correlations between the DNA helical conformations and IBP H-Bonds.The results imply that the IBP H-Bonds is very important factor in determining DNA helical conformations .